How do you know if you need a bigger carb? I went to the track last wednesday and ran a new best (14.5 @ 95) and some old guy came to me and wanted to know what I had done. we got to talking and he said I could probably gain a tenth or twoand a couple of mph by switching to a 750 or so instead of my 625. I only ran once b/c of all the ricers that showed up (I didn't want to sit in line for 30+ minutes) he was suprised I could pull off a 14.x with my 2.73 rear, I thought I did ok since some of you guys run alot faster than me with similar gears :rolleyes: . should I take this carb thing seriously or should I spend my money elsewhere...like gears. :confused:

It's hard to say, but the smaller carb is probably helping with those gears by increasing mixture velocity at lower speeds for more torque. Do you have a vacuum gauge? Hook it up and see how much vacuum you have at WOT. If there's a few inches above zero, you could use more carb, but then again, it may hurt bottom end torque and show no difference. I'd recommend the gears first if you don't need to worry about economy or high speed cruising.

I really don't need to go more than 65 but most times I do ;) . I think I'll go ahead and order a vac guage.

I ran a 13.54 with a 650. I don't think you need a bigger carb.

zz69chevelle has a good point bigger carburetor are not necessarily better for small blocks such as ours, however larger carburetor tends to lose lower end but gain MPH wich indicates more horsepower but we want the lower RPM torque curve to get that all so important 60' foot time low as possible. I assume you have a demon 625 with vacumm secondaries which sounds perfect for your combo and those gears, with 3.55 or 3.73 expect your current 60 foot time to drop therefore resulting in a faster quarter mile time. I would not touch your carburetor leave it alone maybe get 3.55 at most since you have vacumm secondaires, and probably a stall recommended stall 2400 RPM.

being an 8.5" 10 bolt I have a pretty big gap between 3.42 and 3.73. what are your thoughts on that? my new tires are 29" tall and 275mm across now. I think I may even go bigger next time around to a 30" or 31" tall tire and as fat as 290mm. I like big tires. I will for sure buy new gears by the end of this summer. right now I'm at about 2000 rpm at 60. my highway milage when I went to tx over the holiday was 21mpg but going to work and back in the city it's as low as 10mpg graemlins/sad.gif . will lower gears improve my city milage some? if I could get a consistent 15-17 mpg all around it would be less stressful.

If you're going to a taller tire, go with the lower (3.73) gear.

With a 29 inch tire and 3.42s you should theoretically be going around 50 at 2000rpm.

29"/3.73=46ish
30"/3.73= 47ish
31"/3.73= 49ish.

the other side of it would be a 31" with 3.42s. wich would be about 52ish.

so you have a range of about 46-52mph@2000RPM depending on tire/gear combo. Either way, you're well under the 60isMPH you get now.

that puts it into a good perspective(sp?), thanks graemlins/thumbsup.gif